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Results for “Spatial orientation”

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PubMed1995

[Neuropsychological assessment in a patient with left hemineglect syndrome--a case report].

We performed a sequential neuropsychological tests before and after neurosurgical intervention on a 69-year-old patient with left hemineglect syndrome caused by metastatic right temporal papillary carcinoma. The tests performed before operation and computer tomography revealed marked impairment in visuospatial reasoning, spatial orientation, visual perception, visuoconstructional praxis, effort emory, as well as block design in Wechsler Adult Intellectual Scale-Revised, all of which suggested right temporo-parietal lesion. Left spatial neglect was obviously demonstrated by the Line Cancellation Test, Watch Test, and clinical observation. After surgical debulking of the tumor, his performances on most of the tests were improved. Our study demonstrated that the conventional neuropsychological test is not only useful for localizing the cerebral lesion but also valid for the assessment of functional recovery after treatment, a role that can never be replaced by any other modern technique.

Aged↗

PubMed2005

Orienting and alerting: effect of 24 h of prolonged wakefulness.

It is well known that a decrease in vigilance can easily occur during 24 h of continuous wakefulness, but no study has assessed whether and in what way extended wakefulness might affect spatial orienting. In other words, it is not clear what happens when a subject has to orient his attention during a state of poor vigilance, resulting from sleep loss or sustained wakefulness. The aim of this study was to investigate this issue. Twelve right-handed male subjects participated in the experiment, which took place on two consecutive days. On the first day, in order to evaluate baseline orienting attention, the subjects performed a covert orienting task (in which the cue stimuli generated endogenous shifts of attention), lasting 20 min; on the second day, during 24 h of prolonged wakefulness, the same task was performed 12 times, about every 120 min, beginning at 10.00 a.m. Results showed an overall slowing of reaction time across the sessions, indicating a linear decrease of vigilance. However, this vigilance decrease did not seem to affect attention-orienting mechanisms, suggesting that the two systems are independent of each other.

Adult↗

PubMed1995

Effects of the spatio-temporal structure of optical flow on postural readjustments in man.

How does the spatio-temporal structure of an oscillating radial optical flow affect postural stability? In order to investigate this problem, two different types of stimulus pattern were presented to human subjects. These stimuli were generated either with a constant spatial frequency or with a spatial frequency gradient providing monocular depth cues. When the stimulation was set in motion, the gain response of the antero-posterior postural changes depended upon the oscillation frequency of the visual scene. The amplitude of the postural response did not change with the amplitude of the visual scene motion. The spatial orientation of the postural sway (major axis of sway) depended strictly and solely on the structure of the visual scene. In static conditions, depth information resulting from the presence of a spatial frequency gradient enhanced postural stability. When set in motion, a visual scene with a spatial frequency gradient induced an organization of postural sway in the direction of the visual motion. Considering visual dynamic cues, postural instability depended linearly both on the logarithm of the velocity and on the logarithm of the temporal frequency. A nonlinear relationship existed between the amplitude of the fore-aft postural sway at the driving frequency and the temporal frequency, with a peak around 2-4 Hz. These results are discussed in terms of their implications for the separation of visual and biomechanical factors influencing visuo-postural control.

Adult↗

PubMed1984

Scalp potential fields evoked by grating stimuli: effects of spatial frequency and orientation.

Visually evoked potentials were recorded from an array of 16 electrodes over the occipital cortex in 12 subjects. Grating stimuli of different spatial frequencies were presented on a circular test field, and potential fields evoked by vertical, horizontal and oblique stimuli were compared. Component latencies were determined by computing a reference-independent measure of field power. Scalp field maps were constructed at component latencies and compared over all conditions. Significant influences of both spatial frequency and orientation on component latencies were found. Component latencies were shortest for 2.3 c/deg gratings, and for vertically oriented stimuli. Latencies increased for horizontal, and further for oblique, gratings. The effect of spatial frequency or orientation on the location of the major components on the scalp was less pronounced. On the other hand, there were significant differences both in component latency and scalp distribution when upper and lower hemiretinal stimuli were compared. Upper hemiretinal stimulation yielded shorter latencies and a more anteriorly located potential peak on the scalp.

Adult↗

PubMed2003

Visual sensitivity in search tasks depends on the response requirement.

This paper reports a comparison between two tasks of visual search. Two observers carried out, in separate blocks, a saccade-to-target task and a manual-target-detection task. The displays, which were identical for the two tasks, consisted of a ring of eight equally spaced Gabor patches. The target could be defined by a difference from the distractors along four possible dimensions: orientation, spatial frequency, contrast or size. These four dimensions were used as variables in separate experiments. In each experiment, performance was measured over an extensive range of values of the particular dimension. Thresholds were thus obtained for the saccade and the manual response tasks. The nature of the response was found to modify the relative visual sensitivity. For orientation differences, manual response performance was better than saccade-to-target performance. The reverse was true for spatial frequency and contrast differences, where saccade-to-target performance was better than manual response performance. We conclude that saccade-selection in a search task draws on different visual information from that used for manual responding in the equivalent task. The two tasks thus differ in more than the different response systems used: the results suggest the action of different underlying neural visual mechanisms as well as different neural motor mechanisms.

Contrast Sensitivity↗

PubMed1978

Phytohemagglutinin and transmembrane proteins in agglutinated sheep erythrocyte ghost membranes.

Oriented and periodically stacked sheep erythrocyte ghost membrane specimens were prepared by agglutination of the ghosts with phytohemagglutinin M and sedimentation, and were studied by X-ray diffraction. The spatial orientation of the planes of the membranes in the diffracting stack was determined from the lamellar reflections of the periodic stacking. Equatorial diffraction at (10.5 A)-1 and a (1.5 A)-1 reflection were recorded which correlate with side-to-side packed transmenbrane alpha-helices in the agglutinated membrane. A broad (4.6 A)-1 ring with strong equatorial accentuation and broad maxima at about (2.2 A)-1 and (1.2 A)-1 were observed which are attributed to the hydrocarbon chain arrangement in lipid phases of the agglutinated ghost membrane.

Animals↗

PubMed1999

Isodirectional tuning of adjacent interneurons and pyramidal cells during working memory: evidence for microcolumnar organization in PFC.

Studies on the cellular mechanisms of working memory demonstrated that neurons in dorsolateral prefrontal cortex (dPFC) exhibit directionally tuned activity during an oculomotor delayed response. To determine the particular contributions of pyramidal cells and interneurons to spatial tuning in dPFC, we examined both individually and in pairs the tuning properties of regular-spiking (RS) and fast-spiking (FS) units that represent putative pyramidal cells and interneurons, respectively. Our main finding is that FS units possess spatially tuned sensory, motor, and delay activity (i. e., "memory fields") similar to those found in RS units. Furthermore, when recorded simultaneously at the same site, the majority of neighboring neurons, whether FS or RS, displayed isodirectional tuning, i.e., they shared very similar tuning angles for the sensory and delay phases of the task. As the trial entered the response phase of the task, many FS units shifted their direction of tuning and became cross-directional to adjacent RS units by the end of the trial. These results establish that a large part of inhibition in prefrontal cortex is spatially oriented rather than being untuned and simply regulating the threshold response of pyramidal cell output. Moreover, the isodirectional tuning between adjacent neurons supports a functional microcolumnar organization in dPFC for spatial memory fields similar to that found in other areas of cortex for sensory receptive fields.

Action Potentials↗

PubMed1977

Early postnatal developmental changes of the cardiac electric field in guinea-pigs.

Changes of the "representative" maximum spatial cardiac vector were followed daily from the 1st till the 3th postnatal day of life in a group of 70 guinea-pigs. This vector representing the spatial vectorcardiographic loop shifted gradually during the observation period from the right caudal quadrant to the left caudal quadrant attaining its new spatial orientation on the 7th day. This shift is accompanied by a transitory tilt in the cranial direction with a peak on the 7th day and a transitory decrease of the spatial magnitude with a peak on the 4th day. There was no significant difference between the spatial magnitude of the "representative" maximum vector on the 1st and the last (13th) day of observation.

Animals↗

PubMed1981

[The vectorcardiogram pattern of the athlete's heart (author's transl)].

In order to assess the vectorcardiographic pattern of the athlete's heart, we evaluated the vectorcardiograms of 17 professional footballers; the signs of ventricular hypertrophy were particularly studied. 9 athletes had left ventricular hypertrophy, 3 showed VCgraphic signs of combined ventricular hypertrophy and 5 had normal vectorcardiograms. In all athletes with left ventricular hypertrophy the initial forces had normal spatial orientation (I A left ventricular hypertrophy). Likely, the combined right ventricular hypertrophy explains these VCgraphic patterns. The QRS loop did not show abnormal morphology, only the high magnitude of the spatial maximum QRS vectors was significant for diagnosis of left ventricular hypertrophy. The increase of the cardiac volumes induced by training might explain the high magnitude of the QRS loop.

Adult↗

PubMed1995

[Trans-thoracic 3D echocardiography reconstruction for left ventricular volume determination].

2D-echocardiography is a safe and inexpensive method for accurate left ventricular volume quantification. However, accuracy of measurements is limited by the requirement of geometric assumptions and volume computation algorithms. Reproducibility is diminished by erroneous image plane positioning, which is due to the necessity of standardized reference images. The degree of variation can influence clinical decision making. 3D-echocardiography has overcome those problems. Volume quantitation is performed without the need of geometric assumptions, computation algorithms or reference images. The shape of a ventricle is defined by acquired data, not by calculated data. Since the recent development of sophisticated hardware- and software techniques the method can be utilized under clinical circumstances. For data acquisition tomographic planes are acquired either in a random or in a sequential order. For random acquisition the transducer is positioned at various acoustic windows at the thoracic wall and spatial orientation of the corresponding plane is localized by a spark gap device. By this way various, non-parallel cross-sectional images of the left ventricle are acquired. The spatial position of the planes is displayed by lines in a parasternal longitudinal view, each representing a "line of intersection". When tomographic planes are acquired in a sequential manner, mostly rotational scanning is utilized. Here, multiple apical views of the left ventricle are acquired during ECG- and respiration gated rotation of the transducer over a span of 180 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed1995

Immigration--mismatches in labour, housing and space: the effects of immigration of several nationalities with regard to the Netherlands.

"In the Netherlands, the sharp recent increase of the number of refugee immigrants (asylum seekers) runs parallel to increased numbers of immigrants of other types. Therefore, at least five types of immigrants should still be distinguished (labour migrants, migrants from former colonies, from EU countries, from other rich countries, and asylum seekers). Their spatial orientation in the Netherlands (urban, suburban, rural), by choice or by constraint, is the main focus of this study. The outcomes of the immigration processes have been confronted with general and spatial characteristics of the labour market and housing market. Matches and mismatches are discussed."

Demography↗

PubMed2000

Modelling cognitive dysfunctions with bilateral injections of ibotenic acid into the rat entorhinal cortex.

Neurodegenerative diseases, traumatic brain injury and stroke are likely to result in cognitive dysfunctioning. Animal models are needed in which these deficits and recovery of the affected functions can be investigated. In the present study, the entorhinal area was chosen as the target for lesioning and for assessing the lesion-induced deficits in the Morris water maze. The entorhinal cortex is regarded as an interface between the hippocampus and neocortex. Deafferentiating the hippocampus through entorhinal lesions impairs spatial learning. The effects of lesions, induced by either electrocoagulation (experiment 1) or ibotenate excitotoxicity (experiment 2), on spatial orientation behaviour were investigated. Water maze performance after unilateral or bilateral ibotenate injections into the entorhinal cortex was studied in the third experiment. In an additional study, the replicability of the spatial learning deficit after lesions induced by bilateral injections of ibotenic acid into the entorhinal cortex was assessed by comparing the results of nine experiments. We found that spatial learning was impaired after bilateral lesions aimed at the entorhinal cortex. The electrolytic lesion technique produced a relatively large sham effect, whereas the excitotoxic lesioning method did not. Unilateral injections of ibotenic acid into the entorhinal cortex did not affect spatial navigation. The ibotenate-induced lesions replicably produced deficits in the Morris tasks. The degree of the induced spatial learning impairments and the effects on the rate of acquisition during training, however, differed between experiments. This result suggests that the fundamental biological diversity between shipments of rats can account for variation in the effects of parahippocampal damage on spatial learning even in highly standardized experimental set-ups. Rats lesioned by bilateral injections of ibotenic acid into the entorhinal cortex provide an interesting and reliable model for investigating cognitive dysfunctions in neurodegenerative diseases, stroke or traumatic brain injury.

Brain Injuries↗

PubMed1995

Control of Rapid Arm Movements When Target Position Is Altered During Saccadic Suppression.

This experiment examined whether rapid arm movements can be corrected in response to a change in target position that occurs just prior to movement onset, during saccadic suppression of displacement. Because the threshold of retinal input reaches its highest magnitude at that time, displacement of the visual target of a saccade is not perceived. Subjects (N = 6) were instructed to perform very rapid arm movements toward visual targets located 16, 20, and 24 degrees from midline (on average, movement time was 208 ms). On some trials the 20 degrees target was displaced 4 degrees either to the right or to the left during saccadic suppression. For double-step trials, arm movements did not deviate from their original trajectory. Movement endpoints and movement structure (i.e., velocity-and acceleration-time profiles) were similar whether or not target displacements occurred, showing the failure of proprioceptive signals or internal feedback loops to correct the arm trajectory. Following this movement, terminal spatially oriented movements corrected the direction of the initial movement (as compared with the single-step control trials) when the target eccentricity decreased by 4 degrees. Subjects were unaware of these spatial corrections. Therefore, spatial corrections of hand position were driven by the goal level of the task, which was updated by oculomotor corrective responses when a target shift occurred.

Journal Article↗

PubMed1985

A qualitative limitation on visual transfer via the anterior commissure. Evidence from a case of callosal agenesis.

Interhemispheric transfer of visual information was investigated in a patient with agenesis of the corpus callosum. CT scanning, pneumoencephalography, and neuropsychological evaluation failed to reveal any evidence of extracallosal cortical damage. The patient's performance was within normal limits both in the left and right visual fields on tasks requiring identification of briefly presented material. In contrast, his performance was abnormally poor when required simply to detect or localize a dot presented to the right of fixation. Performance with presentations in the left visual field was normal. These findings suggested that the absence of the corpus callosum may result in a selective impairment of visuospatial, but not identification, processes for material initially presented to the left hemisphere. To document this possibility further, the patient was tested on tasks designed to assess these processes simultaneously by requiring him both to identify and judge the exact location of each stimulus presented. Performance was normal in both lateral fields for identification accuracy, but significantly worse in the right visual field for location judgements. A similar pattern of results was found on a task requiring the identification of a stimulus and specification of its spatial orientation. These findings suggest a qualitative limitation on the type of information which may be transferred via the anterior commissure, possibly due to the inability of temporal lobe neurons to encode spatially organized information. Furthermore, the findings suggest that in the normal brain the right hemisphere may be crucially involved in visual attention and spatial functions, regardless of the field of presentation.

Adult↗

PubMed1989

Spatial S-R compatibility with orthogonal stimulus-response relationship.

Spatial stimulus-response (S-R) compatibility with unimanual two-finger choice reactions was investigated under conditions in which the spatial orientation of response keys was either parallel to or perpendicular to the orientation of the stimuli. Subjects responded to green or red lights in the left or right visual field (irrelevant stimulus location). The response keys were oriented horizontally on the left or right side of the body midline parallel to the stimuli, and were pressed with the palms facing down (Condition A), or were oriented orthogonally to the stimuli in the midsaggital plane, either horizontally and pressed with palms facing down (B) or facing up (C), or vertically and pressed with palms facing the body (D). The results for Condition A demonstrate the usual spatial S-R compatibility effect between field of stimulation and spatial position of responding finger. For Conditions B and D, a strong reaction time advantage still obtained for those stimulus-finger pairings that are compatible under Condition A. Condition C revealed an RT advantage for the opposite pairings. This shift of the compatibility effect from Condition B to Condition C indicates that the left/right distinction of fingers does not follow a simple, fixed spatio-anatomical mapping rule. The results are discussed within the framework of a hierarchical model of spatial S-R compatibility, with spatial coding and spatio-anatomical mapping as factors.

Adult↗

PubMed1977

New approach to local thermodilution: use of pig tail catheters to avoid basic difficulties.

The use of pit tail catheters and the placing of the thermistor distal to the lumen for the cold injectate have allowed the development of a new catheter for local thermodilution with many advantages. Apart from its small size and possibility of percutaneous introduction, the spatial orientation of the thermistor to the rest of the catheter and to the port of injection ensures: (a) its absolute thermal insulation; (b) avoidance of contact with vessel walls: and (c) constant spatial relationship between the lumen for injection and the thermistor as regards the dynamics of flow and temperature change.

Animals↗

PubMed2005

[Effects of thyroid hormone on cognitive function in rats with chronic cerebral ischemia].

OBJECTIVE: To study the characteristics of cognitive dysfunction in rats with chronic cerebral ischemia and the effects of thyroid hormone on the rats' cognitive function. METHODS: Thirty-one male SD rats were randomly allocated into normal control group (n=12), operation group (with bilateral carotid artery ligation and examined 5 weeks later, n=6), acute phase treatment group (APT, with bilateral carotid artery ligation and intragastric administration of thyroid hormone at 20 mg once daily for 5 weeks starting from the day of operation, n=7) and chronic phase treatment group (CPT, with the operation and thyroid hormone administration in an identical manner started from the sixth week following the operation, n=6). Morris water maze test was performed at the end of experiment. One-way ANOVA was used to estimate the differences in the learning and memory functions of the rats using SPSS10.0 for Windows. RESULTS: The average latent period of the operation group was significantly prolonged in comparison with that of the other groups (P<0.05) in spatial orientation test. The probe time (time spent in the quadrant where the platform was once situated) of normal control was much shorter than those of the operation, APT and CPT groups in spatial probe test (P<0.05), and the operation group had the poorest score. The average latent period of the operation and CPT was longer than that of the other groups (P<0.05) in working-memory task (P<0.05), and the operation group again had the poorest score. CONCLUSION: Spatial cognitive function is totally damaged in rats with chronic cerebral ischemia, and learning can not induce the formation long-term memory because of short-term memory damage. Thyroid hormone may lessen but can not fully repair the damage of the cognitive dysfunction resulting from chronic cerebral ischemia, and early intervention with thyroid hormone may be beneficial for chronic cerebral ischemia.

Animals↗

PubMed1994

Interocular suppression in the visual cortex of strabismic cats.

Strabismic humans usually experience powerful suppression of vision in the nonfixating eye. In an attempt to demonstrate physiological correlates of such suppression, we recorded from the primary visual cortex of cats with surgically induced squint and studied the responses of neurons to drifting gratings of different orientation, spatial frequency, and contrast in the two eyes. Only 1 of 50 apparently monocular cells showed any evidence of remaining, subliminal excitatory input from the "silent" eye when the two eyes were stimulated with gratings of similar orientation, and even among the small proportion of cells that remained binocularly driven, very few exhibited facilitation when stimulated binocularly. The majority of cells from both exotropes and esotropes, even those that could be independently driven through either eye, displayed nonspecific interocular suppression: stimulation of the nondominant eye with a drifting grating of any orientation depressed the response to an optimal grating being presented to the dominant eye. This phenomenon exhibited a gross nonlinearity in that it was dependent on the temporal sequence of stimulus presentation: stimulation of the nondominant eye caused significant suppression only if the neuron was already responding to an appropriate stimulus in the dominant eye, but not when onset of stimulation in the two eyes was simultaneous. Interocular suppression was always independent of the relative spatial phase of the two grating stimuli, and usually broadly tuned for the spatial frequency of the suppressive stimulus. Suppression may depend on inhibitory interaction between neighboring ocular dominance columns, combined with the loss of conventional disparity-selective binocular interactions for matched stimuli in the two eyes. The similarity of interocular suppression in strabismic cats and that caused by orthogonal gratings in the two eyes in normal cats (Sengpiel and Blakemore, 1994; Sengpiel et al., 1994) suggests that strabismic suppression and binocular rivalry depend on similar neural mechanisms.

Animals↗